Cyanoacrylate adhesives, which contain 2-cyanoacrylate as a major component, have been favorably used as an instantaneous adhesive in wide variety of industries, medical field, leisure activity and household since 2-cyanoacrylate as the major component has the property of easily polymerizing anionically in the presence of a trace amount of moisture and basic substances to quickly cure.
While cyanoacrylate adhesives have excellent moisture and thermal resistance on adherends of rigid PVC, ABS or the like, they are poor in moisture and thermal resistance upon application to materials of nitrogen-containing compounds or sulfur-containing compounds such as chloroprene rubber, EPDM and other synthetic rubbers and Bakelite.
A reason for the poor moisture and thermal resistance in adhesion of cyanoacrylate adhesives to chloroprene rubber, EPDM and other synthetic rubbers and to Bakelite would be that humidity and/or heat promote the nitrogen-containing compounds or sulfur-containing compounds to bleed from these materials and accumulate on the adhesion interface resulting in reduction of adhesion strength and that the bled compounds promote decomposition of cyanoacrylate polymers.
The moisture and thermal resistance of the adhesives is further deteriorated when they are used to bond synthetic rubbers such as chloroprene rubber and EPDM in a state where internal residual stress exists.
The reason is understood as follows:
Hardened bodies of cyanoacrylate adhesives are stiff and are poor in a function of relaxing the internal stress. Thus, it is considered that the effect of stress on adhesion interface and adhesion layer becomes significant, and as a result, deterioration of adhesion caused by humidity and/or temperature is promoted.
Because of these reasons, urethane adhesives, epoxy adhesives, acryl adhesives and the like have been used in the industry for adhesion to sites where durability is required, while hot melt adhesives, pressure-sensitive adhesives and the like have been used for adhesion to sites where flexibility is required.
However, urethane adhesives, epoxy adhesives, acryl adhesives and the like have disadvantages that they are "poor in operability due to requirements of blending of two packages or primer pretreatment of the surfaces to be adhered" and "poor in productivity due to slow adhesion rate." On the other hand, hot melt adhesives and pressure-sensitive adhesives have a disadvantage that they are "poor in durability." In the industry, thus there is a strong demand for development of an adhesive that is excellent in durability and brings about improvement in operability and productivity.
Cyanoacrylate adhesives, which are characterized by single package instantaneous adhesion, may bring about the above-mentioned improvement in operability and productivity, however are poor in durability and flexibility (stress relaxation) as already explained.
For the purpose of providing flexibility with cyanoacrylate adhesives, a known technology is to blend a phthalate, a sebacate, and a saturated copolymer polyester described in JP-A-63-284279.
However, these softening materials adversely affect moisture and thermal resistance since they are present in cyanoacrylate polymers just in dispersed state.
JP-A-58-185666 is another known technology for providing flexibility, which discloses blending a C.sub.1 -C.sub.4 alkyl (meth)acrylate or a C.sub.1 -C.sub.4 alkoxyalkyl (meth)acrylate. These (meth)acrylates not only exist in cyanoacrylate polymers in dispersed state but also have a possibility of improving durability by radical polymerization at elevated temperature.
In the adhesion to chloroprene rubber which contains nitrogen-containing compounds or sulfur-containing compounds, however, the compositions blended with the C.sub.1 -C.sub.4 alkyl (meth)acrylate or the C.sub.1 -C.sub.4 alkoxyalkyl (meth)acrylate described in JP-A-58-185666 can not still satisfy the moisture and thermal resistance.
Under such situations, there is a strong need for developing an instantaneous adhesive-that is excellent in moisture and thermal resistance even on materials said to be difficult to bond, that is, materials that contain nitrogen-containing compounds or sulfur-containing compounds, for example, synthetic rubbers like chloroprene rubber and EPDM, and Bakelite.
The present invention is to provide a cyanoacrylate instantaneous adhesive that has excellent moisture and thermal resistance when applied for adhesion particularly to adherends that contain nitrogen-containing compounds or sulfur-containing compounds, for example, synthetic rubbers like chloroprene rubber and EPDM, and Bakelite.